1. Technical Field of the Invention
The present invention relates to caster rolls used in the manufacturing of sheet material and methods of manufacturing caster rolls. More particularly, the present invention relates to an internally cooled caster roll having one or more layers of material, such as metal, formed on a roll core of the caster roll and methods of manufacturing the caster roll.
2. Description of Related Art
In the manufacture of cast aluminum plate, strip, sheet, or foil (hereinafter referred to as “aluminum sheet material”), conventional roll casting machines used to manufacture such aluminum sheet material typically have a twin-roll arrangement. In the twin-roll arrangement, a pair of substantially parallel, water-cooled, and counter-rotating rolls is used to cast the aluminum sheet material. Generally, after a given period of use, the surface, or roll shell, of these “caster” rolls must be reground and/or repaired because of heat cracks resulting from thermal fatigue and/or out-of-roundness (i.e., eccentricity) due to slipping between the roll core and roll shell. As the roll shell becomes thinner from regrinding, the roll shell surrounding the roll core must be replaced periodically and the roll core repaired before the twin-roll assembly is rebuilt.
It is generally known that the major cause of damage to prior art caster rolls is slipping between the roll core and the roll shell. The roll core in prior art caster rolls typically has circumferential grooves or channels formed in the surface of the roll core. The slipping typically occurs between the grooved or channeled surface of the roll core and the roll shell, which results in the formation of roll gaps between the roll core and roll shell. This leads to the aforementioned out-of-roundness (i.e., eccentricity) problem, which may ultimately result in misshaping the cast aluminum sheet material. Another problem associated with current caster rolls includes cracking in the roll shell due to thermal gradient and accompanying leakage of coolant onto the roll shell, which is a safety concern. Additionally, the thermal gradient along the surface of the roll core and roll core/roll shell slippage often cause the caster roll to distort or bend, which also may result in misshaping the cast aluminum sheet material during production runs.
One approach known in the art for extending the service life of caster rolls is disclosed in U.S. Pat. No. 5,598,633 to Hartz. In the Hartz '633 patent, the surface of the roll core is covered with two overlays of stainless steel each having a distinct hardness. The overlay of stainless steel directly in contact with the surface of the roll core is softer than the second, external overlay of stainless steel. An analogous approach to the foregoing is disclosed in U.S. Pat. No. 5,265,332 also to Hartz. The Hartz '332 patent attempts to extend the service life of the roll core by coating the inner surface of the roll shell with hard chromium.
Internally cooled rolls are well known in the field of continuous sheet casting machines. For example, U.S. Pat. No. 5,279,535 to Hawes et al. discloses an internally cooled caster roll for use in continuous sheet casting applications that includes a plurality of longitudinally extending coolant-conveying bores that extend the length of the caster roll. An annular manifold in the form of an end cap is secured within a recess formed in each end face of the caster roll and defines a plurality of discreet pathways, which places the open ends of the longitudinally extending bores in fluid communication with one another. The end caps additionally define a pathway formed to place the open end of one bore in fluid communication with a coolant inlet or coolant outlet passageway of the caster roll. A similar cooling roll having longitudinally extending cooling channels is disclosed in published International Application No. PCT/EP01/09818 (WO 02/26425).
U.S. Pat. No. 5,209,283 to Miltzow et al. discloses a caster roll comprising a roll core with a plurality of threads and a threaded sleeve, which threads onto the threaded roll core. The threaded connection between the roll core and roll sleeve defines a spiral channel through which a cooling medium flows to cool the caster roll. A similar “threaded” roll core is disclosed in U.S. Pat. No. 5,292,298 to Scannell.
U.S. Pat. No. 4,944,342 to Lauener discloses a continuous caster roll for casting aluminum sheet material. The caster roll is comprised of a roll shell enclosing a roll core. Cooling medium flows through axial cooling channels defined in the outer surface of the roll core. A counter flow principle is applied in the caster roll in which the cooling medium alternately flows in the cooling channels from one end of the caster roll to the other.
Further, U.S. Pat. No. 4,773,468 also to Lauener, discloses a method for extending the service life of a caster roll. In the caster roll disclosed by the Launer '468 patent, a plurality of rods is placed axially in grooves formed in the roll core of the caster roll. The rods protrude radially outward from the roll core and a roll shell is shrink-fitted onto the rods. As the roll is used in production runs, the roll shell wears and once the wear has proceeded to a predefined lower limit, the rods are replaced and a new roll shell is shrink-fitted onto the rods. Other references in the field of internally cooled caster rolls include U.S. Pat. No.: 5,887,644 to Akiyoshi et al.; U.S. Pat. Nos. 2,850,776; 2,790,216; and 2,664,607 all to Hunter. The disclosure of each of the references identified hereinabove is incorporated into this disclosure by reference.
The foregoing references disclose various prior art arrangements and methods for manufacturing, internally cooling, and generally extending the service of caster rolls. Nonetheless, a need still exists for a reduced cost, internally cooled caster roll having an extended service life between roll shell replacements. Additionally, a need exists for a roll shell replacement method that reduces the costs associated with roll shell replacements generally, which is the primary capital outlay required to extend the service life of caster rolls.